A lead frame forms the base or skeleton of an IC package, providing mechanical support to semiconductor dies during assembly into a finished package. A lead frame typically includes a die paddle for attaching a semiconductor die, and leads providing the means for external electrical connection to the die. The die can be connected to the leads by wires, e.g. through wire bonding or tape automated bonds. Lead frames are typically constructed from flat sheet metal, e.g. by stamping or etching. The sheet metal is typically exposed to chemical etchants that remove areas not covered by photoresist. After the etching process, the etched frames are singulated (separated) into lead frame strips. Each lead frame strip includes a number of unit lead frames each having the die paddle and lead construction described above.
Semiconductor dies attached to the die paddles after completion of the assembly process of a lead frame strip are usually tested after separation of the unit lead frames from the lead frame strip, e.g. by punching. Alternatively, the unit lead frames remain mechanically connected to the lead frame strip by tie bars during die testing. This is commonly referred to as lead frame strip testing. Separation of the unit lead frames from the lead frame strip occurs after electrical testing. The die paddles remain electrically connected to the lead frame strip by the tie bars during testing. This is problematic for applications where the die paddles serve an electrical connection function, e.g. in DSO (dual small outline) packages where the exposed die paddles provide an electrical connection to the backside of semiconductor dies attached to the die paddles. In this case, the tie bars electrically short the die paddles to the lead frame strip and to other die paddles attached to the same lead frame strip, complicating the electrical testing process. Electrical isolation is also required for other lead frame processing such as partial plating and electrical charge processes.